Plants for Erosion Control
Plants that aid with erosion control help to prevent soil from being blown away by wind or from becoming damaged and depleted by water and runoff. Soil is far more than just dirt and we need to protect it. One key thing in protecting the soil is to keep bare soil to a minimum and keep a living root in the soil for as much of the year as possible. But due to their growth habit or root system, certain plants are especially useful for placement on a slope.
Using Plants to Prevent Erosion on Your Land
Using plants to prevent erosion on your land can be important for long-term health and stability. In permaculture, we seek to create sustainable systems that will endure and erosion is a threat to stability within the systems you seek to create.
But what exactly is erosion? What causes it? What factors come into play when it comes to the speed and severity of these processes? And how precisely can plants help us to tackle this problem? In this article, we will take a look at each of these questions, and provide you with some strategies to help you choose plants to protect the soil where you live.
What is Erosion?
Erosion is the movement of soil or rock from one location to another.
Most frequently, when we talk about erosion in the context of land management we are referring to soil erosion – when friable surface soil is displaced by the wind, water flow, animal or human activity, and deposited in a different location.
In permaculture land management, protection of our precious soils is of paramount concern. Soil, as we soon learn when we delve deeper into permaculture in theory and practice, as far more than just 'dirt'.
Soil is a living ecosystem, teeming with life. Healthy soil means healthy plants means healthy people. Everything comes back to the soil, and our very existence depends on it, which is one of the reasons why it is so important that we do all we can to protect it, and prevent it from simply being washed, blown and trampled away.
Erosion is one form of soil degradation that we do our best to curtail or avoid. It is a form of soil degradation that can significantly damage topsoil, reducing productivity and ecological stability on farms and in gardens. Ultimately, the end result of soil erosion is desertification.
Excessive soil erosion is a significant global problem. Around the world, soils are being degraded through erosion and other issues at an alarming rate. Halting this issue is a pressing concern, both on a very local and on a global scale.
Fortunately, there are many measures that we can take to limit it where soil vulnerability is found. Using plants to prevent erosion is one of the most important strategies we can employ on a permaculture property.
In order to understand how to do so, however, we first need to understand the processes at work, the factors that affect soil erosion, and the roles that plants can play in tackling this issue.
What Causes Erosion?
Typical causes of erosion are surface processes . Most commonly, erosion is of most concern on steeper slope. A number of factors relating to the environmental conditions, degree of slope, and properties of the soil determine the rate of erosion and how much material is lost.
Typical causes of erosion are:
- Water, ice or snow.
- Air flow and wind.
- Animal grazing and activity.
- Anthropocentric (e.g. tillage erosion)
Rainfall and surface runoff can cause splash, sheet, rill or gully erosion (increasing in severity from the first form to the last listed).
Erosion also occurs along rivers and streams, and along valleys or other areas where flooding may occur. And Tidal waters can also cause erosion of coastlines.
Wind erosion is also known as aeolian erosion. This is of particular concern in arid and semi-arid regions, and during periods of drought can be most pronounced.
There are two main types of wind erosion: deflation, where loose soil particles become airborne, and abrasion, where particles carried by the wind wear down surfaces.
Soils can also be eroded by animals, as they undertake their natural activities. Though this tends to become a major problem only when animals kept by humans overgraze an area of land, or are overstocked, becoming too numerous for the vegetation on a site to be maintained. If you keep livestock on your property then this could be another cause of soil erosion to consider.
Humans are responsible for a massive increase in the rate at which soil erosion is occurring around the world.
Intensive agricultural practices, such as tillage, human-caused deforestation and ecosystem degradation, roads and urban sprawl and construction, acid rain, and anthropocentric climate change all have a role to play in increasing global rates of soil degradation.
Factors that Affect Soil Erosion
Climate change of one key factor that determines the rate at which soil is eroded.
As most people are no doubt aware, climate change caused by human activity influences rainfall in profound ways. And since water is a major cause of erosion, the increasing prevalence of flooding and other extreme weather events also increases the potential for soil erosion on a site.
(As I write, we are under a warning of flooding in our area – something increasingly common as global temperatures continue to rise.)
Elsewhere, meanwhile, water shortage and drought can also lead to increased wind erosion and also make soil more vulnerable to other causes of erosion.
Of course, the plants we choose for our gardens, homesteads, smallholdings or farms can help us to both mitigate climate change and adapt to its effects.
So broadly speaking, planting to sequester as much carbon as possible (carbon gardening or carbon farming) can help reduce the impacts of climate change, including increasing soil erosion.
So choosing plants for carbon sequestration – plenty of trees, shrubs and other perennial plants – is one step in using plants to prevent erosion on your land.
Other key factors that affect the erosion of soils include:
- The amount of vegetative cover on the soil.
- The structure and composition of the soil itself.
- The topography of a site and the degree of slope.
So beyond understanding that we should plant in general, keeping a living root in the soil for as much of the year as possible and avoiding large areas of bare soil, we should also think more specifically about how precisely we can use plants to address specific problems.
Using Vegetative Cover to Protect the Soil
Before we start to look at the use of specific plants, it is helpful to note that vegetation in general protects the soil below from erosion.
Plant cover – of any kind – increases the permeability of the soil to rainwater, decreasing runoff. It acts as a protective layer over the soil surface, preventing particles from being eroded by wind.
It adds organic matter to the soil over time, forming a blanket over bare soil, while roots below the surface anchor the soil in place, weaving together to make the soil more stable, and less prone to all forms of erosion.
This means that when soil is left bare, or vegetative cover is lost, this opens the door for erosion to occur.
Selecting a high proportion of perennial plants (that will remain in place over multiple years), and, in annual production, carefully planning the gardening or farming year, sowing successionally, and using green manures and cover crops, can reduce bare soil and help prevent erosion.
Using Plants To Improve Soil Structure
Light, friable, silty or sandy soils are most vulnerable to many forms of erosion, though heavier clay soils can also become compacted and waterlogged make runoff more likely.
Understanding your soil type is key to determining the problems that you are likely to face, and the plants that could form at least part of a solution.
The composition, moisture content, organic matter content and degree of compaction in your soil will determine its resistance to erosion. Choosing the right plants can help to improve the soil where you live, and make it less vulnerable to different types of erosion.
The right plants can draw water from the soil through transpiration, preventing waterlogging and runoff, or ensure that sufficient soil moisture remains through shading soil to reduce evaporation, for example.
Deciduous trees and shrubs and herbaceous perennials increase soil organic matter as they lose their leaves or die back each year.
This increase in organic matter in the soil improves soil structure, and boosts microbial life and other life in the soil that helps with water infiltration and transportation, and binds soil particles together to form aggregates with nets and glue-like structures.
Carefully selecting plants to boost microbial life is important, since not only the plant cover but also the quality and health of the soil web is crucial to reduce different forms of erosion.
The plants might boost microbial life, forming symbiotic relationships with soil biota while in active growth. But you might also choose plants to provide biomass to use in mulches that can be laid over the surface of the soil, between plants, to further protect and enhance the soil over time.
To give one example, growing trees to provide ramial wood to chip or shred and lay as mulch can help you to build fungal ecology in the soil on your property.
Fungal hyphae create nets to increase soil stability, coated in glomalin that glues soil together and helps with the formation of aggregates to reduce vulnerability to erosion.
Using Plants for Slope Stability
If you are dealing with slope on your property, it is important to understand that a steeper slope increases the velocity of surface runoff and can increase erosivity. The longer and steeper a slope, the higher the rates of erosion can be – especially if the land is denuded of vegetation.
In permaculture, we may sometimes utilise earthworks to reduce slope and perhaps, for example, terrace the site to reduce water flow and increase utility. But selecting plants for slope is also an important part of the puzzle.
Selecting the right plants, and combinations of plants to reduce erosion and increase soil stability on a slope can be a rather complex process.
Generally speaking, however, when choosing plants for slope, we need to think first and foremost about the root structure of the plants.
For slope stabilisation, we typically need a combination of roots that reach to different depths, to stabilise different layers of the soil.
We need plants with deep tap roots and extensive root systems that delve right down into the soil of the slope. But we also frequently also need to consider shallower, fibrous-rooted plants to stabilize the top layers of the soil.
Deep roots and extensive root systems can act like piles and buttresses to stabilize steep slopes, and help to prevent mudslides, landslips etc..
And shallow fibrous rooted plants with a complex fretwork of fine roots may help to keep the surface together and prevent surface erosion. This is most apparent where the root systems of plants with fine roots are consistently distributed, creating a network with an effect comparable to a geotextile mesh.
Erosion is more likely to be limited when both deeper and shallower rooted species are utilised in planting on a slope – deeper rooted species anchoring the deeper soil layers, while finer rooted shrubs, grasses etc/ create a stabilizing effect in the upper 1m or so of the rhizosphere.
Using Plants to Reduce Wind
As we have learned above, wind is often a major cause of erosion – especially in more arid conditions and where soils are light and silty or sandy.
As well as thinking about placing plants on the specific area where soil erosion is taking place, we might also think about placing plants to reduce the wind causing the erosion. Sometimes, revegetation may prove challenging without additional measures within the wider landscape.
Wind can potentially damage or knock down trees or other plants designed to stabilize a slope, and wind throw on trees due to the force of the wind can exacerbate erosion issues and other instability issues on slopes.
Wind break hedges and shelter belt tree-lines can help to reduce wind in a particular part of your property, and may help in lessening the impact of wind on the soil and plants.
Using Plants To Manage Water Flow
Another thing to think about is how specific plants can be chosen to manage the flow of water down a slope, and on your property in general.
Slowing water with terracing or keyline design on steeper terrain, and with on-contour swales, for example, on gentle slopes can be part of the puzzle. But planting is also key when it comes to managing water flow to control and limit soil erosion.
Planting certain vegetation on slopes can reduce soil moisture preventing the erosion that occurs in wet conditions. As a general rule, higher root density within the rhizosphere on a slope results in lower soil water content. This, in turn, leads to an increase in shear strength and a decrease in soil permeability – factors which make a slope less prone to failure and erosion.
Shading that plants can provide also prevents desiccation of soils that could cause more erosion to take place in drier areas. And good ground cover with vegetation in general can keep more moisture in the soil, preventing runoff that leads to erosion.
Of course, even when earthworks are also part of the solution to prevent erosion on slopes due to water flow and runoff, planting these earthworks with appropriate plants is key to success.
Plant Selection for Pasture/ Forage Management
If you keep livestock on your property, it will of course be necessary to keep the appropriate number of animals for the space available, and to rotate grazing, browsing and foraging to maintain existing vegetation and avoid denuding the soil.
It can also be crucial, however, to think carefully about the plants that you choose for pasture. Making the right choices will make it easier to maintain a sward (ground covering pasture) and keep other plants standing.
Choosing the right mix of grasses, forbs and legumes, and/or other plants like shrubs and trees for your animals will be crucial as you seek to keep soil covered to avoid soil erosion.
Selecting Plants To Avoid Tillage Erosion
To prevent erosion on farms and in gardens, it is important to protect and enhance the soil by taking a no dig or no till approach. This involves taking steps and choosing growing methods that allow you to leave the soil as undisturbed as possible.
Tilling disrupts fragile soil ecology, and degrades the soil over time – exposing it and leading to erosion during the plowing period.
Instead of tilling, we can adopt an approach to keep living roots in the soil, and the soil covered with vegetation. We can use cover crops etc.. and diversify when it comes to our plant choices and growing methods.
To avoid the damage done by intensive agriculture or gardening methods to the soil, we can adopt an agroecological approach, and embrace perennial food production in place of mono-crop arable farming or growing annual crops. We can turn to agroforestry and consider forest gardening, silvo-arable and/or silvo-pasture schemes.
By refusing methods and practices that damage the soil (tilling, pesticide and herbicide use, use of synthetic fertilizers) and adopting sustainable alternatives, we can make sure that the soil will be there to continue to feed and support us for many years to come.